In the field of magnetic heads to be mounted on a magnetic recording apparatus such as a hard disk drive (HDD), recently, the recording method is being shifted from longitudinal recording to perpendicular recording in order to improve the recording density with respect to a magnetic recording medium such as a hard disk. The perpendicular recording method achieves high linear recording density and also has an advantage that the recording medium after recording becomes highly resistant to heat fluctuation.
A perpendicular recording magnetic head is provided with a coil film for generating a magnetic flux and a magnetic pole film for guiding the magnetic flux to a recording medium. The magnetic pole film is constituted by a plated film formed by electroplating on an electrode film intended to function as a seed film.
In the meantime, improvement in recording capacity of a hard disk drive (HDD) requires not only to increase the track density by reducing the magnetic pole film width at the magnetic head but also to improve the recording resolution by increasing the coercive force of the medium.
In order to assure sufficient overwrite characteristic (OW) with respect to a medium of such a high coercive force, the magnetic head must have a main magnetic pole film with a high saturation magnetic flux density. In the prior art, accordingly, a plated film forming a main portion of the main magnetic pole film is made of a high saturation magnetic flux density material, such as a FeCo material, a CoNiFe ternary alloy film, and a high saturation magnetic flux density material such as Fe, and FeN, and the electrode film intended to function as a seed film is also made of a high saturation magnetic flux density material. For example, Japanese Unexamined Patent Application Publication No. 2006-253252 discloses a main magnetic pole in which a FeCoNi plated film is formed on a FeCoNi electrode film. It describes that the saturation magnetic flux density (Bs) of the main magnetic pole reaches 2.4 T.
On the other hand, Japanese Unexamined Patent Application Publication No. 2006-269690 discloses a main magnetic pole film in which a FeCo alloy plated film is formed on a non-magnetic conductive layer and then used as an electrode film for formation of a FeNi alloy plated film thereon. In this case, the saturation magnetic flux density of the FeCo alloy electrode film (plated film) is approximately 2.4 T (tesla), while the saturation magnetic flux density of the FeNi alloy plated film is approximately 2.0 T (tesla). Replacing the FeCo alloy plated film with a FeCoNi alloy plated film is also expected, and in this case, the saturation magnetic flux density is approximately 2.3 T (tesla).
In the perpendicular recording magnetic head, however, merely increasing the saturation magnetic flux density is not sufficient, and it is also necessary to avoid the “pole erase” phenomenon in which a signal recorded on a magnetic recording medium by the main magnetic pole film becomes erased when recording is not performed.
In the perpendicular recording magnetic head, the main magnetic pole film for recording has its hard axis directed along an air bearing surface to perform recording in magnetization rotation mode. That is, residual magnetization along the air bearing surface is minimized to prevent an excess magnetic flux from being emitted when recording is not performed, thereby avoiding the pole erase. In order to assure this function, the coercive force Hc of the main magnetic pole film has to be kept low.
In the prior art, however, higher saturation magnetic flux density is aimed not only for the plated film as a main portion of the main magnetic pole film but also for the electrode film as a seed film therefor, and therefore the electrode film is generally made of a magnetic material, as disclosed in Japanese Unexamined Patent Application Publication Nos. 2006-253252 and 2006-269690. A magnetic film having an increased saturation magnetic flux density also has an increased coercive force. Thus, the problem of pole erase has not been dealt with satisfactorily.
Although some prior art documents are conscious of the problem of pole erase, they are consistent in that the electrode film is made of a magnetic material and deal with it by decreasing the saturation magnetic flux density of the plated film, which inevitably sacrifices the overwrite characteristic.
Discussing respective magnetic pole films made of, for example, FeCo, FeCoNi and NiFe alloys from the viewpoint of the coercive force Hc, at first, the pole erase characteristic obviously deteriorates in a magnetic pole film in which a FeCoNi alloy plated film with a saturation magnetic flux density of 2.3 T is formed on a FeCo alloy electrode film with a saturation magnetic flux density of 2.4 T, while sufficient overwrite characteristic can be obtained. This is because Hc of the electrode film of 2.4 T is larger than Hc of the electrode film of 2.3 T.
In a magnetic head in which a magnetic pole film that is a FeNi alloy plated film with a saturation magnetic flux density of 2.0 T is formed on a FeCo alloy electrode film with a saturation magnetic flux density of 2.4 T, the pole erase characteristic can be assured, but the overwrite characteristic is insufficient to obtain a much higher recording density.
In a magnetic head in which the electrode film and the plated film are made of a FeCo alloy with a saturation magnetic flux density of 2.4 T, the overwrite characteristic can be improved, but the pole erase characteristic decreases because the FeCo alloy is a material from which excellent soft magnetic properties are inherently difficult to obtain.
In a magnetic head in which the electrode film and the plated film are formed by a FeNi alloy plated film with a saturation magnetic flux density of 2.0 T, the pole erase characteristic can be improved because the coercive force is low, but the overwrite characteristic deteriorates.
In a magnetic head in which the electrode film and the plated film are formed by a FeCoNi alloy plated film with a saturation magnetic flux density of 2.3 T, improvement in overwrite characteristic can be expected, but the characteristic margin decreases as compared with a FeNi alloy plated film with a saturation magnetic flux density of 2.0 T from the viewpoint of the pole erase characteristic.
Furthermore, since the film peeling of the electrode film has to be avoided to achieve a stable head production process, a film structure which increases the adhesion strength of the electrode film has to be obtained in addition to reducing the coercive force as described above.